This is definitely done in the research world. The flash/brightness from the arc isn't an issue because it's a different wavelength (UV vs. IR).

certainly in the immediate vicinity of the arc. the secret would be to accommodate for that in the exposure. you're also going to throw out the most energetic parts of the spectrum with a filter.

idk if thermal would be that useful for steel, especially if you can clearly resolve the boundary of the melt pool - but for high conductivity metals like copper and aluminum, it might be a real godsend. the problem with these is that since they wick heat away, you need to build up the temperature of the whole piece until its close to melting, and then just push it over with the arc. its pretty common to take it too far and have a big section of work turn into a slaggy mess.